linux-kernel - Re: [PATCH v3 5/7] usb: dwc3: Add snps,ref-clock-frequency-hz property for ACPI

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Message-ID: <CAHp75VeDs6f7euqsZ2fmD42V2M6eWf1_CQPXyr-GfF0HVWA+Vg@mail.gmail.com>
Date:   Fri, 4 Feb 2022 21:24:25 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Sean Anderson <sean.anderson@...o.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        Robert Hancock <robert.hancock@...ian.com>,
        Baruch Siach <baruch@...s.co.il>,
        Felipe Balbi <balbi@...nel.org>,
        Thinh Nguyen <Thinh.Nguyen@...opsys.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Balaji Prakash J <bjagadee@...eaurora.org>
Subject: Re: [PATCH v3 5/7] usb: dwc3: Add snps,ref-clock-frequency-hz
 property for ACPI

On Fri, Feb 4, 2022 at 8:44 PM Sean Anderson <sean.anderson@...o.com> wrote:
> On 2/4/22 1:38 PM, Andy Shevchenko wrote:
> > On Fri, Feb 4, 2022 at 6:00 PM Sean Anderson <sean.anderson@...o.com> wrote:
> >> On 2/4/22 7:54 AM, Andy Shevchenko wrote:
> >> > On Thursday, January 27, 2022, Sean Anderson <sean.anderson@...o.com <mailto:sean.anderson@...o.com>> wrote:

...

> > In order to have more or less unified APIs in the future I would
> > suggest using 'clock-frequency' for the "main" functional clock. For
> > example, 8250_dw uses it for the baud rate generator, while it also
> > utilizes auxiliary clock(s) on some platforms.
>
> OK, I had a look though that driver, and it seems like it uses
> clock-frequency only for the baudclk, and e.g. apb_pclk has no
> corresponding frequency property. For this driver, it would mean that
> the suspend clock would only be configurable through device tree. Is
> that the approach you recommend?


What I meant is to use the "clock-frequency" property as it is kinda
standard de facto for the "main'' functional clock. The rest is up to
the individual drivers. From the API perspective I would expect a
common helper in the future that takes clock name and returns rate
based on clock (if found) or "clock-frequency" property. We may also
extend in far future to support any combinations of the [clock name,
property name] to get a clock rated either via Device Tree or via
ACPI.

-- 
With Best Regards,
Andy Shevchenko